Boromirs way?

[Celegorm]

I always thought, I know LotR. But a few days ago a friend asked, why did Boromir needs so long to get from Minas Tirith to Imladris.
This is referring to the quote:

'In this evil hour I have come on an errand over many dangerous leagues to Elrond: a hundred and ten days I have journeyed all alone.'

It's about 1100 miles from Minas Tirith to Rivendell, so why does he needed that long?
The roads are dangerous, OK. And he doesn't know the exact location of Rivendell.
But 110 days!!!
Do you have any suggestions?